Shanks v. Klein was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner who was being held in a federal prison. The case arose when a prisoner, William Shanks, was held in a federal prison in the state of Illinois. Shanks sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals. The Court also noted that the writ of habeas corpus was a remedy that could only be used to challenge the legality of a person's detention, and not to challenge the conditions of the detention. The Court's decision in Shanks v. Klein established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal prisons. This decision has been cited in numerous subsequent cases, and has been used to support the principle that state courts cannot interfere with the federal government's authority to imprison individuals.

In Shanks v. Klein, the Supreme Court was tasked with determining whether a contract between two parties could be enforced when it had been made without consideration and in violation of an existing statute. The majority opinion held that the contract was unenforceable due to its lack of consideration and statutory infraction. Justice Field dissented from this decision, arguing that although there may have been no consideration for the agreement, both parties were still bound by their promises as they had voluntarily entered into them with full knowledge of all relevant facts. He further argued that even if one party violated a statute while entering into such an agreement, it should not necessarily render it void or unenforceable since statutes are enacted for public policy reasons rather than to protect private interests; thus any breach would only affect those who chose to enter into such agreements despite knowing about said laws beforehand.